Compound structure made of composite material and method of production

ABSTRACT

Compound structure made of composite material, such as fiber-reinforced polymer resin, comprising first oblong elements reciprocally distanced and parallel to each other and second oblong elements reciprocally distanced, parallel to each other and crisscrossed with respect to the first oblong elements. The first oblong elements and the second oblong elements are made in a single body to define a reticular structure with a monolithic flat shape

FIELD OF THE INVENTION

The present invention concerns a compound structure made of compositematerial and the corresponding method of production.

In particular, the compound structure, hereafter also called grille,according to the present invention can be provided with reinforcementfibers such as glass fibers, carbon fibers, boron fibers or aramidfibers and polyester resins.

The present invention is applied, although not exclusively, in compoundstructures for walkable floors such as gangways, stairs, parapets,covers for basement windows or windows in general, or to make fences,gates or for structural elements such as formworks, sluice gates orfloors.

BACKGROUND OF THE INVENTION

Compound structures made of composite material are known, also calledpultruded grilles, reinforced with fibers and normally consisting ofparallel bars connected to each other by round pieces glued or wedgedtransverse to the parallel bars.

Reinforced plastic grilles are also known, consisting of monolithicarticles made by molding, also large-sized, with different types ofmesh, different thickness of the bars and different thickness of thearticle.

It is known that, depending on use, a grille must have resistance to thestresses to which it is subjected during use.

Within the framework of grilles made of polymer resins, it is known toincrease their resistance by incorporating fibers, for example glassfibers, carbon fibers, and aramid fibers, also known commercially asKevlar® fibers. Grilles made of fiberglass or PRFG are known, forexample, that is, a plurality of glass fibers incorporated in polyesterresins.

The grille is obtained using known molding techniques, molding a polymerresin which, polymerizing, incorporates inside itself the fiberspresent, generating the grille with predefined mechanical properties.

Known grilles normally consist of a series of first oblong elements anda series of second oblong elements made in a single body to define areticular structure.

The first oblong elements are disposed substantially parallel with eachother in a first direction, while the second oblong elements aredisposed substantially parallel with each other in a second direction,orthogonal to the first direction. In this way the first and secondoblong elements define the reticular structure with a plurality ofapertures or cavities.

Since the oblong elements are in practice made by molding, they have arectangular cross section, or trapezoid with a slight angle that allowsthem to be removed from the mold, and have no undercuts. In particular,the trapezoid section provides opposite inclined sides to define aremoval angle of about 2°-3° to allow the grille to be removed from themold.

A typical example of a grille used for example for walkways is definedby a reticular mesh with a square shape and a side of about 38 mm,having a height/thickness of about 38 mm and a thickness of the oblongelements that varies from 5 mm of the lower side to 7 mm of the upperside.

Known grilles are particularly heavy, however, and this often conflictswith the need to reduce the overall weights.

Furthermore, known grilles have poor resistance to mechanical stressesand, if it is necessary to reach high bearing capacities, an extremelyheavy and expensive grille will be required, with a large quantity ofmaterial required to make it.

Grilles are also known which consist of the reticular structuredescribed above, on a flat surface of which a continuous flat layer iscoupled in a single body or glued, to close, on the side of the flatsurface, the apertures or cavities defined between the oblong elements.When it is made in a single body with the oblong elements, the flatlayer is reinforced with glass fibers of the “mat” type, and givesfurther bearing capacity to the article.

However, this solution is particularly expensive due to the largequantity of material used, and is extremely heavy.

One purpose of the present invention is to obtain a compound structurethat is less heavy than similar compound structures in the state of theart, with the same properties of mechanical resistance. Merely by way ofexample, one purpose of the present invention is to make a compoundstructure which, with the same resistance and rigidity, has a saving inweight of at least 20%-30% or more.

Another purpose of the present invention is to make a compound structurethat has greater structural properties of resistance to mechanicalstress than in the state of the art. In particular, another purpose ofthe present invention is to make a compound structure in which thecapacities of bearing resistance on a vertical plane are increased.

Another purpose is to perfect a method to make a compound structure withproperties of mechanical resistance that are equal to or greater than aknown compound structure with the same weight.

Another purpose of the present invention is to drastically reduce theproduction times of a compound structure, with the advantage of reducedproduction costs.

The Applicant has devised, tested and embodied the present invention toovercome the shortcomings of the state of the art and to obtain theseand other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independentclaims, while the dependent claims describe other characteristics of theinvention or variants to the main inventive idea.

In accordance with the above purposes, a compound structure made ofcomposite material, such as fiber-reinforced polymer resins, comprisesfirst oblong elements reciprocally distanced and parallel to each otherand second oblong elements reciprocally distanced and parallel to eachother and crisscrossed with respect to the first oblong elements.

The first oblong elements and second oblong elements are made in asingle body to define a reticular structure with a monolithic flatshape.

According to one aspect of the present invention, at least one of eitherthe first oblong elements or the second oblong elements have a crosssection that is T-shaped and/or L-shaped, that is, defined by a firstportion with an elongated quadrangular shape and by a second portionwith an elongated quadrangular shape, and wherein the first portion islocated incident against the second portion.

This particular T- and/or L-shaped configuration of the cross section ofthe oblong elements allows to obtain a compound structure that islighter than state-of-the-art structures with the same mechanicalresistance. This leads to a reduced quantity of material needed to makethe compound structure and therefore to lower costs of the raw materialused. Furthermore, with this solution the oblong elements have acontinuous cross section and are not joined in the longitudinaldirection, which is usually more stressed.

Forms of embodiment of the present invention also concern a method formaking a compound structure of composite material, such asfiber-reinforced polymer resins, which provides to make in a single bodyfirst oblong elements reciprocally distanced and parallel to each otherand second oblong elements reciprocally distanced and parallel to eachother and crisscrossed with respect to the first oblong elements todefine a reticular structure.

According to one aspect of the present invention, the method provides tomake at least one of either the first oblong elements or the secondoblong elements with a cross section that is T-shaped and/or L-shaped.

Other forms of embodiment of the present invention concern an apparatusfor making a compound structure that comprises at least one molddefining a molding cavity in which to dispose at least one material tomake the compound structure. The molding cavity is defined by aplurality of first oblong grooves made reciprocally distanced andparallel to each other, and by a plurality of second oblong grooves madereciprocally distanced and parallel to each other and crisscrossed, withno break in continuity, with respect to the first oblong grooves.

According to one aspect of the present invention, at least one of eitherthe first oblong grooves or the second oblong grooves have a crosssection that is T-shaped and/or L-shaped.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will becomeapparent from the following description of some forms of embodiment,given as a non-restrictive example with reference to the attacheddrawings wherein:

FIG. 1 is a perspective view of a compound structure according to thepresent invention;

FIG. 2 is an exploded perspective view of a compound structure accordingto a variant of FIG. 1;

FIG. 3 is a cross section of a compound structure in the variant in FIG.2;

FIG. 4 is a schematic illustration of a cross section of an apparatusfor making a compound structure according to the present invention;

FIG. 5 is an exploded perspective view of a compound structure accordingto another variant;

FIG. 6 is a section of a compound structure according to the variant inFIG. 5;

FIG. 7 is a section of a compound structure according to anothervariant.

To facilitate comprehension, the same reference numbers have been used,where possible, to identify identical common elements in the drawings.It is understood that elements and characteristics of one form ofembodiment can conveniently be incorporated into other forms ofembodiment without further clarifications.

DETAILED DESCRIPTION OF SOME FORMS OF EMBODIMENT

According to the present description and with reference to FIG. 1, theinvention concerns a compound structure 10 made of composite material.

The compound structure 10 comprises a plurality of first oblong elements11 reciprocally distanced and parallel to each other and a plurality ofsecond oblong elements 12 reciprocally distanced and parallel to eachother.

The second oblong elements 12 are made in a single body and crisscrossedwith respect to the first oblong elements 11 to define a reticularstructure 13 with a flat shape.

According to the solution shown in FIG. 1, the second oblong elements 12are located orthogonal to the first oblong elements 11, which allows tomake uniform the mechanical resistance of the compound structure 10 inall the directions of the plane.

According to some forms of embodiment of the present invention, thecrisscrossed disposition of the first oblong elements 11 and the secondoblong elements 12 allows to define between the latter apertures orcavities 22 that confer the grille structure.

The apertures 22 can have a rectangular or square shape if the firstoblong elements 11 and second oblong elements 12 are disposedsubstantially orthogonal to each other, and they can have a rhomboid orparallelogram shape if they intersect each other by an angle other than90°.

The reticular structure 13 has a first flat surface 14 and a second flatsurface 15, opposite the first flat surface 14.

The first flat surface 14 and/or the second flat surface 15 can besmooth, or can be irregular, rough or knurled with an anti-slipfunction.

According to one aspect of the present invention, at least one of eitherthe first oblong elements 11 or the second oblong elements 12 have across section that is T-shaped or L-shaped (FIG. 1).

The T- or L-shaped cross section confers on each oblong element 11and/or 12 a greater bearing capacity of resistance to stresses, and inparticular to flexional stresses compared with known solutions where thetransverse elements have a substantially rectangular shape.

The more it is possible to take material distant from the neutral axis,the more a T- or L-shaped cross section can maximize the resistance of astructural element to vertical stresses. And the more it is possible todistribute the material symmetrically with respect to the neutral,horizontal axis, the more the overall weight of the reticular structure13 is reduced.

In this way it is possible to obtain, given the same weight, a compoundstructure 10 with much greater resistance than state-of-the-art compoundstructures. Moreover, thanks to this, given the same mechanicalresistance, it is possible to reduce the overall weight of the compoundstructure 10, and also the quantity of material used to make it, whichalso gives advantages in terms of production costs.

According to a possible variant, shown in the attached drawings, boththe first oblong elements 11 and the second oblong elements 12 have aT-shaped and/or L-shaped cross section. This solution allows to makeuniform the bearing capacity of the compound structure 10 in thedirections lying on a plane.

By T-shaped or L-shaped cross section we mean a section defined by afirst portion 16 and a second portion 17, both with an elongatedquadrangular shape, and wherein the first portion 16 is located incidentagainst the second portion 17.

In the case of a T-shaped cross section, the first portion 16 is locatedincident against the second portion 17 in an intermediate zone of thelatter.

In the case of an L-shaped cross section, the first portion 16 islocated incident against the second portion 17 in an end edge of thelatter.

According to possible forms of embodiment, the first oblong elements 11and the second oblong elements 12 can have the L-shaped section incorrespondence with the perimeter edges of the reticular structure 13,while the other oblong elements 11, 12 have a T-shaped cross sectionshape.

According to a possible solution, the first oblong elements 11 and thesecond oblong elements 12 can have a thickness of the cross sectioncomprised between about 3 mm and 10 mm, preferably between 4 mm and 8mm, and a height of the cross section comprised between 20 mm and 50 mm,preferably between 25 mm and 45 mm.

The first portion 16 of the first oblong elements 11 and second oblongelements 12 is disposed with its elongated development incident towardthe first flat surface 14, while the second portion 17 of the firstoblong elements 11 and second oblong elements 12 is disposed with itselongated development parallel to the second flat surface 15.

The first portions 16 of the first oblong elements 11 and second oblongelements 12 define with one of their sides the first flat surface 14,while the second portions 17 define with one of their sides the secondflat surface 15.

According to the form of embodiment shown in FIG. 1, the first portion16 is defined by two bigger sides 18, equal in size and opposite eachother, and by a pair of smaller sides, that is, a first smaller side 19and a second smaller side 20 connected to the bigger sides 18 and havingsmaller sizes than them.

The second smaller side 20 is connected to the second portion 17, whilethe first smaller side 19 faces toward the first flat surface 14. Thefirst smaller sides 19 of the first portions 16 define the first flatsurface 14.

According to a possible solution, the second smaller side 20 is biggerthan the first smaller side 19 and the bigger sides 18 are disposedconverging with respect to each other toward the first smaller side 19.The first portion 16 has a substantially trapezoid shape, with thesmaller base facing toward the first flat surface 14.

The trapezoid shape allows to define a removal angle for the possibleextraction of the compound structure 10 from a mold during theproduction steps as described hereafter.

According to a variant, the first smaller side 19 and the second smallerside 20 can be the same size, so that the first portion 16 issubstantially a rectangle.

The second portion 17 is defined by two bigger sides 21, of which one isconnected to the first portion 16 and the other facing and defining thesecond flat surface 15 of the reticular structure 13.

According to the form of embodiment shown in FIG. 1, the second portion17 is substantially rectangular in shape, although other shapes are notexcluded, for example trapezoid, in which the bigger side 21 definingthe bigger base of the trapezium is associated with the first portion 16and the bigger side 21 defining the smaller base of the trapezium facestoward the second flat surface 15.

According to a possible variant shown in FIGS. 2 and 3, the compoundstructure 10 comprises a first reticular structure 13 a and a secondreticular structure 13 b, substantially analogous to the abovedescription referring to the reticular structure 13 in FIG. 1, and areoverlapping and reciprocally coupled.

According to a possible solution, the first reticular structure 13 a andsecond reticular structure 13 b are substantially identical, so thatthey can completely overlap. Or it can be provided that the distancesbetween the first oblong elements 11 and the distances between thesecond oblong elements 12 are substantially identical for the firstreticular structure 13 a and the second reticular structure 13 b.

This solution allows to define a compound structure 10 with asymmetrical distribution of the weight and material with respect to itsneutral axis which in this case corresponds to the join plane betweenthe first reticular structure 13 a and the second reticular structure 13b. This solution allows to obtain a compound structure 10 with isotropiccharacteristics of mechanical resistance.

In some variants, the first reticular structure 13 a and the secondreticular structure 13 b have different geometric sizes of the firstoblong elements 11 and the second oblong elements 12.

According to this variant, it can in any case be provided to distributethe material symmetrically with respect to the neutral axis which inthis case may not correspond to the join plane between the firstreticular structure 13 a and the second reticular structure 13 b. Inthis case it is possible to obtain a compound structure 10 withorthotropic characteristics of mechanical resistance. This lastcharacteristic can also be defined by different widths and/or lengths ofthe first portions 16 or second portions 17 of the oblong elements 11,12.

According to a possible solution, the coupling of the first reticularstructure 13 a and the second reticular structure 13 b is obtained bygluing. This solution allows to obtain the first reticular structure 13a and the second reticular structure 13 b in a monolithic body withgreat mechanical resistance.

Gluing can be carried out using vinyl ester glues, epoxy glues etc.,while the compound structure 10 is made with isophthalic, bisphenol ororthophthalic resins. In particular, it may be provided to use gluingresins similar to the material of the first reticular structure 13 a andthe second reticular structure 13 b, and/or to use thickened resins.

Gluing is obtained in such a manner as to support the shear stressesencountered with the horizontal section. Indeed, as is known, shearstresses are normally much smaller than the traction and compressionstresses caused by the flexion of vertically stressed elements.

According to a variant, the coupling of the first reticular structure 13a and the second reticular structure 13 b can be achieved withmechanical connections, for example threaded connections, brackets,nails, rivets or suchlike.

According to the solution shown in FIG. 2, the first reticular structure13 a and the second reticular structure 13 b are coupled to each otherwith the respective first flat surfaces 14.

According to a possible solution, the first reticular structure 13 a andthe second reticular structure 13 b are coupled by overlapping the firstportions 16 of the first reticular structure 13 a above the firstportions 16 of the second reticular structure 13 b.

According to one solution, the first portions 16 of the first reticularstructure 13 a are located completely overlapping the first portions 16of the second reticular structure 13 b, in particular in correspondencewith their first smaller sides 19. This solution allows to increase theinterface surface between the first reticular structure 13 a and thesecond reticular structure 13 b, in this way also increasing theresistance of reciprocal connection between them.

Furthermore, this solution allows to define cross sections of thecompound structure 10 shaped like a double T or a C, and therefore acompound structure 10 able to resist stresses, for example flexional,acting on the first flat surface 14 or the second flat surface 15,irrespective of the specific installation mode.

The cross sections of the compound structure 10 shaped like a double Tare defined by coupling the first oblong elements 11 and the secondoblong elements 12 of the first reticular structure 13 a with those ofthe second reticular structure 13 b.

This solution allows to obtain a compound structure 10 which otherwise,with a simple molding operation, would be unobtainable because of theundercuts that are defined between the first reticular structure 13 aand the second reticular structure 13 b.

FIGS. 5 and 6 show another variant of a compound structure 10 comprisingat least one reticular structure 13 as defined above and a flat element23 overlapping and coupled with a surface, for example with either thefirst flat surface 14 or the second flat surface 15. In this way, it ispossible to define a bearing structural part, defined by the at leastone reticular structure 13, and a walking plane, defined by the flatelement 23.

According to some forms of embodiment of the present invention, the flatelement 23 can be made with polymer resins, for example fiber-reinforcedto give greater mechanical resistance. It is advantageous to provide,for example, that the material that the flat element 23 is made of issubstantially identical to, or at least compatible with, the materialthat the reticular structure 13 is made of. This facilitates for examplethe gluing operations of the reticular structure 13 and the flat element23. Merely by way of example, the flat element 23 can be made ofcomposite material reinforced for example with glass fibers, carbonfibers, Kevlar or other reinforcement material. However, it cannot beexcluded that, in other forms of embodiment, the flat element 23 can bemade of low-cost plastic material, for example polyethylene, polyamide,ABS, PVC or suchlike.

According to some variants, the flat element 23 can be made of differentmaterials, other than plastic, for example wood or its derivatives.

The flat element 23 can have different sizes, starting from a tileformat, for example 250 mm-300 mm per side, and can also have the samesize as the reticular structure 13, which merely by way of example canbe 1220 mm in width and 3360 mm in length, or more. In this case aplurality of flat elements 23 can be associated on the reticularstructure 13, 13 a, 13 b.

The reticular structure 13, 13 a, 13 b, merely by way of example, canhave a thickness S comprised between 20 mm and 60 mm.

The flat element 23 can have a thickness or height H comprised between 5mm and 15 mm, in the case shown here, about 8 mm.

The flat element 23 can have a smaller thickness than the reticularstructure 13, which in practice has a structural support function andcollaborates in improving bearing capacity.

The flat element 23 can have different colors, which can give thecompound structure 10 and the article on which it is installed aparticular esthetic value.

The flat element 23 can be coupled with the reticular structure 13 bymechanical connections, for example by bolting, or alternatively bygluing as described above, by broaching, using pins interposed betweenthe two components.

The flat element 23 in turn defines a support surface, or a walkablesurface, and gives greater structural rigidity to the compound structure10.

The final result is therefore a compound structure 10 which can functionas a flooring and can vary from very elegant to simply functional, withmechanical characteristics similar to comparable state-of-the-artarticles, but much less heavy, even in the order of 30% or more.

According to the form of embodiment shown in FIGS. 5 and 6, the flatelement 23 has a reticular conformation defined, in a single body, byfirst segments 44 and second segments 45, having an oblong developmentand disposed crisscrossed with respect to each other.

According to the form of embodiment shown in FIGS. 5 and 6, at leastsome of the first segments 44 and the second segments 45 are disposed ina position coordinated with the first oblong elements 11 and/orrespectively with the second oblong elements 12.

In particular, it can be provided that at least some of the firstsegments 44 are positioned resting on the first oblong elements 11and/or at least some of the second segments 45 are positioned resting onthe second oblong elements 12.

It is advantageous to provide that the first segments 44 and the secondsegments 45 are positioned resting with their whole surface developmenton the first oblong elements 11 and/or on the second oblong elements 12.

In the solution shown in FIG. 6, the first segments 44 and the secondsegments 45 overlap the first portions 16 of the first oblong elements11 and/or the second oblong elements 12.

If they are connected in a single body, for example by gluing, the flatelement 23 and the reticular structure 13 are sized so as to obtain asymmetrical distribution of the material with respect to the neutralaxis of the whole compound structure 10. Consequently, the section sizesof the oblong segments 44 and 45, and those of the oblong elements 11and 12, can be suitably sized.

The first oblong elements 11 are distanced from each other by a firstdistance D1. Merely by way of example the first distance D1 can becomprised between 80 mm and 160 mm, preferably between 100 mm and 140mm.

The second oblong elements 12 are distanced from each other by a seconddistance D2. According to the solutions shown here, the second distanceD2 is substantially equal to the first distance D1, even though it isnot excluded that it may have different sizes, for example bigger orsmaller.

In the solutions shown in the drawings, the first oblong elements 11 andthe second oblong elements 12 can have a first distance D1 and a seconddistance D2 of 120 mm×120 mm.

The first segments 44 are distanced from each other by a first pitch P1.Merely by way of example the first pitch P1 can be comprised between 15mm and 60 mm, preferably between 20 mm and 50 mm. According to apossible solution, the first distance D1 is comprised between about 1and 5 times the first pitch P1.

The second segments 45 are distanced from each other by a second pitchP2.

According to the solutions shown here, the first pitch P1 issubstantially equal to the second pitch P2, even though it is notexcluded that it may have different sizes, for example bigger orsmaller.

According to a possible solution, the second distance D2 is comprisedbetween about 1 and 5 times the second pitch P2.

In the case shown in FIG. 6, the reticular structure 13 comprises oblongelements 11, 12 with a T-shape and an L-shape in the edges; they have aheight of 32 mm and a pitch between the oblong elements 11 and 12 of 120mm; the flat element 23 has a thickness of 8 mm and a pitch between theoblong segments 44 and 45 of 40 mm, that is, one third the pitch betweenthe oblong elements 11 and 12. This allows the oblong elements 11 and 12to be joined with the oblong segments 44 and 45 every three of thelatter. With this conformation Applicant has obtained a greater rigidityof the compound structure with a saving in weight of about 30%.

In another variant shown in FIG. 7, the compound structure 10 comprisesthe first reticular structure 13 a associated with the second reticularstructure 13 b, in substantially the same way as described above withreference to FIGS. 2 and 3.

The flat element 23 is associated to at least one of either the firstreticular structure 13 a or the second reticular structure 13 b, on thesurface that faces toward the outside during use, with a conformationsubstantially similar to that described above.

According to the solution shown in FIG. 7, the flat element 23 isassociated with the second flat surface 15 of the first reticularstructure 13 a.

In particular, the flat element 23 can rest only on the first reticularstructure 13 a, or it can be attached to it by gluing, or withmechanical connection elements.

In this case the flat element 23 can have the function of dividing thestresses and an esthetical function, without collaborating with thesupport structure below.

In the solution shown in FIG. 7 as well, the flat element 23 comprisesfirst segments 44 and second segments 45 disposed according to areticular configuration.

At least some of the first segments 44 and second segments 45 arelocated resting, with their whole surface development, on the firstoblong elements 11 and/or the second oblong elements 12 of the reticularstructure 13 a or 13 b.

Forms of embodiment of the present invention also concern an apparatus25 for making a compound structure 10 shown schematically in FIG. 4.

The apparatus 25 comprises at least one mold 26; in this case acounter-mold 27 is also shown, able to be selectively coupled with themold 26.

The mold 26 and counter-mold 27 are configured to define between them amolding cavity 28 into which the fibers are disposed to make a compoundstructure 10 as described above.

The molding cavity 28 is defined by a plurality of first oblong grooves29, reproducing in negative the first oblong elements 11 of the compoundstructure 10, and by a plurality of second oblong grooves 30,reproducing in negative the second oblong elements 12 of the compoundstructure 10.

The first oblong grooves 29 are made reciprocally distanced and parallelto each other.

The second oblong grooves 30 are made reciprocally distanced andparallel to each other and crisscrossed, with no break in continuity,with respect to the first oblong grooves 29.

The second oblong grooves 30 can be located substantially orthogonal tothe first oblong grooves 29.

According to the present invention, at least one of either the firstoblong grooves 29 or the second oblong grooves 30 have a T- or L-shapedcross section as defined above with reference to the first oblongelements 11 and the second oblong elements 12.

The T- or L-shape consists of a first portion 31 and a second portion32, transverse with respect to the first portion 31. The configurationand disposition of the first portion 31 and the second portion 32 of thefirst oblong grooves 29 and the second oblong grooves 30 issubstantially equal to that of the first portion 16 and the secondportion 17 of the first oblong elements 11 and the second oblongelements 12 of the compound structure 10.

According to one solution shown in FIG. 4, the first oblong grooves 29and the second oblong grooves 30, and therefore the molding cavity 28,are made completely in the mold 26, disposing the second portion 32facing toward the outside. This prevents defining undercuts, andtherefore disadvantages connected to the subsequent extraction of thereticular structure 13, 13 a, 13 b from the mold 26. This solutionallows to define a mold 26, or matrix, upended compared with traditionalsolutions, which allows to position the fibers with a variabledistribution in predefined positions depending on particularrequirements. In this way it is possible to define zones of thereticular structure 13, 13 a, 13 b with differentiated resistances inthe section of the oblong elements.

Forms of embodiment of the present invention also concern a method formaking a compound structure 10. The method provides to make in a singlebody a plurality of first oblong elements 11 and a plurality of secondoblong elements 12 with configurations similar to what was describedabove to define the reticular structure 13.

Examples of how to make the reticular structure 13 include injection or“Resin Transfer Molding” (RTM), infusion, press molding, hand molding orother types. The monolithic reticular structure 13 can be obtained in anopen mold or closed mold.

Forms of embodiment of the present invention also concern a method formolding compound structures 10 with an apparatus 25 as described above.

A possible molding method can comprise, merely by way of example:

-   -   positioning reinforcement fibers inside the first oblong grooves        29 and second oblong grooves 30 of a molding cavity 28;    -   possibly coupling the counter-mold 27 and the mold 26 to define        the molding cavity 28;    -   filling the molding cavity 28 with polymer resins in a viscous        state to incorporate the reinforcement fibers;    -   polymerizing the polymer resin;    -   extracting the reticular structure 13.

It is clear that modifications and/or additions of parts may be made tothe compound structure 10 of composite material and its method ofproduction as described heretofore, without departing from the field andscope of the present invention.

For example, according to a variant, not shown, instead of having areticular conformation, the flat element 23 can be defined by a platewith a substantially uniform thickness that is coupled above thereticular structure 13, 13 a, 13 b.

The surface of the flat element 23 that faces, during use, toward theoutside, that is, is not directly coupled with the reticular structure13, 13 a, 13 b, can be provided irregular, rough or knurled with ananti-slip function.

It is also clear that, although the present invention has been describedwith reference to some specific examples, a person of skill in the artshall certainly be able to achieve many other equivalent forms ofcompound structure 10 made of composite material and its method ofproduction, having the characteristics as set forth in the claims andhence all coming within the field of protection defined thereby.

1. Compound structure made of composite material, such asfiber-reinforced polymer resin, comprising first oblong elementsreciprocally distanced and parallel to each other and second oblongelements reciprocally distanced and parallel to each other andcrisscrossed with respect to the first oblong elements, said firstoblong elements and said second oblong elements being made in a singlebody to define a reticular structure with a monolithic flat shape,wherein at least one of either said first oblong elements or said secondoblong elements have a cross section shape defined by a first portionwith an elongated quadrangular shape and by a second portion with anelongated quadrangular shape, and wherein the first portion is locatedincident against the second portion.
 2. Compound structure as in claim1, wherein both the first oblong elements and the second oblong elementshave a cross section shape defined by said first portion and said secondportion.
 3. Compound structure as in claim 1, wherein said reticularstructure has a first flat surface and a second flat surface oppositethe first flat surface, wherein said first portion is disposed, with itselongated development, incident toward the first flat surface and saidsecond portion is disposed, with its elongated development, parallel tosaid second flat surface.
 4. Compound structure as in claim 3, whereinsaid first portion of the first oblong elements and the second oblongelements is disposed with its elongated development incident toward thefirst flat surface, and said second portion of the first oblong elementsand the second oblong elements is disposed with its elongateddevelopment parallel to said second flat surface.
 5. Compound structureas in claim 1, wherein it comprises a first reticular structure and asecond reticular structure overlapping and reciprocally coupled. 6.Compound structure as in claim 5, wherein said first reticular structureand said second reticular structure are glued.
 7. Compound structure asin claim 3, further comprising a first reticular structure and a secondreticular structure overlapping and reciprocally coupled, and whereinsaid first reticular structure and said second reticular structure arecoupled to each other with the respective first flat surfaces, to definecross sections of the compound structure shaped like a double T or a C.8. Compound structure as in claim 1, wherein it comprises at least oneflat element overlapping and coupled with a surface of said reticularstructure.
 9. Compound structure as in claim 8, wherein said flatelement is glued to said reticular structure.
 10. Compound structure asin claim 8, wherein said flat element is defined by a plate. 11.Compound structure as in claim 8, wherein said flat element has areticular conformation, defined in a single body by first segments andsecond segments having an oblong development and disposed crisscrossedwith respect to each other.
 12. Compound structure as in claim 11,wherein at least some of the first segments and the second segments aredisposed in a coordinated position with the first oblong elements and/orrespectively with the second oblong elements.
 13. Compound structure asin claim 11, wherein said first oblong elements are distanced from eachother by a first distance and said first segments are distanced fromeach other by a first pitch, said first distance being comprised betweenabout 1 and 5 times the first pitch, and wherein said second oblongelements are distanced from each other by a second distance and saidsecond segments are distanced from each other by a second pitch, saidsecond distance being comprised between about 1 and 5 times said secondpitch.
 14. Compound structure as in claim 5, wherein it comprises atleast one flat element overlapping and coupled with a surface of saidreticular structure, and wherein said flat element is associated to atleast one of either the first reticular structure or the secondreticular structure, on the surface that faces toward the outside duringuse.
 15. Method for making a compound structure of composite material,such as fiber-reinforced polymer resin, which provides to make in asingle body first oblong elements reciprocally distanced and parallel toeach other and second oblong elements reciprocally distanced andparallel to each other and crisscrossed with respect to the first oblongelements to define a reticular structure, wherein it provides to make atleast one of either said first oblong elements or said second oblongelements with a cross section shape defined by a first portion with anelongated quadrangular shape and by a second portion with an elongatedquadrangular shape, and wherein the first portion is located incidentagainst the second portion.
 16. Method as in claim 15, wherein a firstreticular structure and a second reticular structure are overlapping andreciprocally coupled.
 17. Method as in claim 16, wherein said firstreticular structure and said second reticular structure are glued. 18.Method as in claim 16, wherein said first oblong elements and saidsecond oblong elements of said first reticular structure are coupled tothose of said second reticular structure so as to define cross sectionsof the compound structure shaped like a double T or a C.
 19. Method asin any claim from 15, wherein at least one flat element overlaps and iscoupled with said reticular structure.
 20. Apparatus for making acompound structure as in claim 1, comprising at least a mold defining amolding cavity in which to dispose at least one material to make saidcompound structure, said molding cavity being defined by a plurality offirst oblong grooves made reciprocally distanced and parallel to eachother, and by a plurality of second oblong grooves made reciprocallydistanced and parallel to each other and crisscrossed, with no break incontinuity, with respect to the first oblong grooves, wherein at leastone of either the first oblong grooves or the second oblong grooves havea cross section with a shape defined by a first portion with anelongated quadrangular shape, and by a second portion with an elongatedquadrangular shape, and wherein the first portion is located incidentagainst the second portion.
 21. (canceled)